Octane monitoring

ABSTRACT

MEANS TO DETERMINE A CHARACTERISTIC OF A HYDROCARBON, SUCH AS THE OCTANE RATING OF GASOLINE, BY REACTING KNOWN AMOUNTS OF THE HYDROCARBON WITH AN OXYGEN CONTAINING GAS, SUCH AS AIR, UNDER CERTAIN CONDITIONS TO MAINTAIN A MILD REACTION LESS VIGOROUS THAN AN EXPLOSION OR EVEN A COOL FLAME. THE AMOUNT OF OXYGEN CONSUMED IS DIRECTLY CORRELATABLE TO THE CHARACTERISTIC OF INTEREST.

June 12, 1973 a P. CUNNINGHAM ETAL 3,738,808

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Non 4 N /ft i Q United States Patent fice 3,738,808 OCTANE MONITORING Glenn P. Cunningham, Gibsonia, and John G. Larson,

Pittsburgh, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa.

Filed Mar. 18, 1971, Ser. No. 125,687 Int. Cl. G01n 33/22 U.S. Cl. 23-230 PC 14 Claims ABSTRACT OF THE DISCLOSURE Means to determine a characteristic of a hydrocarbon, such as the octane rating of gasoline, by reacting known amounts of the hydrocarbon with an oxygen containing gas, such as air, under certain conditions to maintain a mild reaction less vigorous than an explosion or even a cool flame. The amount of oxygen consumed is directly correlatable to the characteristic of interest.

This invention pertains to the analysis of hydrocarbons, and in particular it pertains to such analysis by means of mildly chemically reacting such substances so as to maintain reaction conditions less violent than an explosion and less violent than even a cool flame. The method includes separating and correlating the amount of oxygen consumed to some characteristic of the original hydrocarbon Substance. The correlation can be performed With the use of calbration curves, or by direct comparisons with results obtained from similar standardized substances having known values of the Characteristics of interest.

It is an object of the invention to provide method and apparatus of the character described adapted to determine the octane rating of gasolines. In the following description the invention is described in terms of an octane monitor for gasoline. It is anticipated that octane determination Will be the most important use of the invention. However, it is thought that the invention is operable to determine other Characteristics of other hydrocarbon substances. For example, the invention could possibly be used in determining the cetane rating of diesel fuel, or With any refinery process, in blending operations, or others, involving a hydrocarbon stream.

Heretofore, there was not a completely satisfactory method of measuring the Octane rating of gasoline. It is tremendouslyy important to the refiner to accurately know the octane rating of his gasoline. In order to assure minimum ratings, and to accommodate inaccuracies in existing techniques, the refiner usually blended the final gasoline so that its octane rating exceeded the minimum specificaton. This practice costs refiners a great deal of money. For example, as an indication of orders of magnitude only, this excess Octane rating can cost as much as $O.25 per barrel of blended gasoline.

There are presently available two basic types or general classes of methods of measuring octane rating. The -first and more basic method is, generally, to burn the gasoline in a special engine, and to then detect the sound of knocking. This system is very slow, expensive in that it requires a skilled operator, not adapted to on-stream operation, requires frequent and expensive maintenance, experiences ditficulty in holding engine conditions constant between the tests due to "drifting of the engine, and is subject to the objection that sound per se is a difiicult parameter to handle scientifically. However, the industry accepted standard is an engine method, and the standardized fuels used in the method of the invention Patented June 12, 1973 and in the second general class of analytical techniques, are standardized by this system. Still within this first class of octane determination methods and apparatus are those devices which built up from an engine by automating it, in various ways, thus removing or diminishing the disadvantage of having to have an operator present. Most of the other disadvantages of the basic engine method still apply to automated engines, perhaps the most important one of which is the difliculty of on-stream application.

The second broad class of Octane determination techniques do not use an engine, but rather operate on the gasoline itself in various different manners. The present invention is of this general class. At present, the most popular such technique reacts gasoline With air in a specific type of Chamber under controlled and Variable flow, temperature, and pressure conditions so as to produce a cool flame in the chamber. A cool flame is a chemical reaction less violent than an explosion, but more violent than the rnild reactions used in the present invention and is characterized by the production of a characteristic luminosity, i.e., a certain kind of light production. The principle of operation is to detect this light or the heat accompanying it, and to then adjust flow rate, pressure, and/or temperature to hold the area of luminosity or cool flame at a constant physical location within the chamber. The amount of adjustment of outside parameters needed to hold the cool flame steady, in response to compositional changes in the gasoline being analyzed, Which reflect as factors tending to move the cool flame in the chamber, is correlatable to the Octane rating or changes in the octane rating of the Substance under analysis.

These cool flame based systems sutfer from many problems. First, as will be developed more in detail below, a cool flame is inherently an unstable phenomenon. Thus, operation of such methods and apparatus is at all tirnes critical and extremely sensitive. The apparatus itself must be vertically Oriented so as to eliminate any gravity eifects on the cool flame region which has a different density than the remainder of the substances in the reactor. Another disadvantage of cool flame based techniques is that they are one step further removed from the reaction than is the present invention. That is, in the present invention the oxygen consumed itself is correlated to the final characteristic of interest. In these prior methods it is some outside parameter, which has some effect on the reaction, which is correlated to the final characteristic of interest. Thus, the advantages of the present invention over the prior art of its general type include that it provides methods and apparatus Which operate in a broad reaction region as opposed to the narrow and unstable cool flame region and is therefore not highly critical in operation, easier to use, and more "forgiving of minor errors. The reactor used in the present invention is completely insensitive to and unefected by orientation. The method of the invention is more directly related to the physical reaction taking place in that the oxygen consumed is correlated to the final result.

The invention provides a dual apparatus to permit smultaneous handling of a standard and a sample to thereby remove the effect of most if not all extraneous factors Which could otherwise lead to incorrect Octane ratings or other results. Examples of such extraneous influences which are eliminated include automatic compensation of temperature Variations; minor amounts of contaminants in the oxygen containing gas, such as might be caused by incomplete removal of trace amounts of oil which might be in the air supply; atmospheric pressure changes, all extraneous iniluences on the analytical device used to measure the quantity of oxygen consumed, and the ability to easily and automatically calibrate or zero the overall apparatus even during the course of operation. This apparatus can also =be used in a single stream mode.

The underlying lbasis of the present invention is the discovery that when a gasoline or other hydrocarbon is mildly reacted with an oxygen containing gas under certain conditions selected to keep the reaction less vigorous than either an explosion or a cool flame, the amount of oxygen consumed is directly correlatable to the Octane rating of that gasolne, or to some other characteristic of interest of said other hydrocarbon.

The above and other advantages of the invention will be pointed out or will lbecome evident in the following detailed description and claims, and in the accompanying drawing also forming a part of the disclosure, in which: FIG. 1 is a schematic diagram of an apparatus which has been built to successfully test the invention; and FIGS. 2 and 3 are diagrams useful in explaining the basis of the method of the invention.

Referring now in detail to the drawing, reference numeral generally designates apparatus which has been built and tested and embodies the invention. The hydrocarbon to be analyzed is supplied in a conduit 12 via a suitable pump, flow control means, and associated equipment, all generally designated by reference numeral 14. One critical part of the apparatus 14 is that a constant and known quantity of fuel be supplied via a conduit 16 to a coil 17 in a pre-heater portion 18 of an oven 21. A conduit 20 Supplies air or other oxygen containing gas from a suitable source not shown via apparatus 22 which includes means to control and measure the flow and the |pressure of the air, and to dry the air. As is known to those skilled in the art, drying includes not only removal of water ibut also removal of C02 and all other contaminants. The clean and dry air is supplied via a branching conduit 24 to a pair of coils 25 in pre-heatet' portion 18.

While air has been used in testing the invention, and it is anticipated that air will be used generally because of its easy availability and low price, it is of course within the scope of the invention to use any other oxygen containing gas. In any case, the amount of oxygen in the gas, which must be known in order to determine the 02 consumed, will be a |known percent of the gas. Therefore, the effective result is to supply a known amount of 02. If desired, pure 02 probably could be used. Air is preferred because it is cheaper, easier to handle and measure, and because the nitrogen in the air might be needed for the proper operation of other parts.

As shown in the drawing the apparatus 10 is set up to operate in dual mode. To this end, a second supply of fuel in a conduit 12a is provided via apparatus 14a and line 16a to a coil 17a in the pre-heater portion 18 of furnace 21. As is obvious, the dual system thus provided could be used for either the dual mode shown, or in single mode by simply not supplying fuel via conduit 1211 and apparatus 14a. In the following description only half the apparatus will -be specifically described, it being understood that the other half is identical. Said other half will be indicated on the drawing with the same reference numerals followed by a. Where there is a difference in structure or operation, the diference will be pointed out.

The conduits 16, 1611, and 24 carrying the fuel and air respectively pass separately through the pre-heater and are heated therein to the temperature within the oven 21. The function of the pre-heater portion is to stabilize reactor conditions by vaporizing the fuel before it passes into the reactor.

The conduits 16 and 24 pass from the pre-heater portion 18 into a reactor portion 26 wherein the fuel, now vaporized, and the air are combined and reacted together. The preferred reaction temperature, for gasoline, is 325 C., with an operative range of 275 C. to 350 C. Tests have shown that above about 350 C. the reaction becomes unstable, and it probably enters the cool flame or even the explosion zone, as will appear below. At temperatures less than 275 C. the reaction is not sufliciently vigorous to yield meaningful results. Of course, different temperatures and ranges Will be needed for different hydrocar- 'bons. The reaction is carried out at or near atmospheric pressure via the analyzer 40 described below.

All reactor products exit from reactor 26 via a conduit 28 which includes a cold trap 30, a water trap 32, and a C02 trap 42. The function of cold trap 30 is to condense and remove all reaction products that will condense at or above -78 C. In handling gasolines, theoretically only CO and C02 flow out of conduit 28 after cold trap 30. The water trap 32, which be any suitable material such as Drierite, is provided to assure that all the water is in fact removed prior to the reaction products being analyzed. The C02 trap 42 is provided because the particular 02 analyzer 40 used could be harmed by C02. In the test apparatus which has been built, C02 trap 42 comprised simply a'container of Ascarite.

In apparatus built in successfully testing the invention, cold trap 30 was at first a Dry Ice-acetone bath, and after further development took the form of automatic refrigeration equipment of the type used in household refrigerators and the like. Each reactor 26 took the form of about 30 inches of coiled Stainless steel pipe having a 'Ma inch inside diameter. The pre-heater took the form of coiled portions of conduits 16 and 24. Oven 21 was thermostated for 325 C. Many other different specific forms of apparatus will be obvious to those skilled in the art.

Analyzer 40, in the form used, comprises an oxygen analyzer, which was manufactured by Teledyne Analytical Instruments Company of San Gabriel, Calif., their Model Number 326M. The analyzer, and the entire system via the analyzer, operates at atmospheric pressure via the analyzer atmospheric vent 44. Other oxygen analyzers are commercially available, any could be used, and some of them may include integral apparatus to serve the function of cold trap 30, C02 trap 42, and/or water trap 32. The results determined by oxygen analyzer 40 are read out on a recorder 46. Two recorders, or one dual pen recorder, is required, and also including a variable span adjustment and Variable zero adjustment. In the embodiment |built in successfully testing the invention, such a recorder manufactured by the Leeds and Northrup Company of Philadelphia, Pa., their Model H AZAR was used.

In single mode operation, i.e., use of only one half of the apparatus shown in FIG. 1, the apparatus is first zeroed by passing oxygen containing gas only, no fuel, through the system, and adjusting recorder 46 to a zero reading. The unreacted stream is made to correlate with the full scale of recorder 46, which is normally units. Now fuel is added via conduit 12, the oxygen containing gas stream remaining unchanged. We have provided that the flow of the oxygen containing gas remains unchanged even though total mass of reactants after reactor 26 increases, by use of the flow control in apparatus 22. The oxygen and fuel react, the system reaches equilibrium, and the reading on recorder 46 stabilizes at some value less than full scale, or 100 units. It is at this stage that the Variable span of the recorder 46 is utilized. The reading on recorder 46 drops because some of the oxygen is going into the reaction products and thus there is less free oxygen. Means, which may be simply a hand subtraction or a table, are provided to change this new reading into some number proportional to the amount of oxygen consumed. For example, if the zero reading was 100 units, and the reading after equilibrium were 60 units, then 100 units minus 60 or 40 units would be proportional to the oxygen consumed and the octane rating of that fuel. Calibration tables can be generated, using standard fuels with known octane ratings, to correlate the readings proportional to volume of oxygen consumed to octane rating.

In tests of the invention, results ranging from plus or minus .2 to plus or minus .5 of an octane number Were determined using 1970 CRC leaded reference fuels.

In dual mode use, the standard fuel is first fed through both halves thereby producing an octane difference of zero. After switching one side to the unknown, the results read directly in octane difference, Which may be then algebrically added to the known Octane rating of the standard to arrive at the octane rating of the un-known. As is known to those skilled in the art, a calibration curve, produced by running several fuels of known octane rating, could be used at this point. The dual mode will produce better results with respect to outside influences on the system. For example, results in single mode could be effected by contaminants in the air supply. This source of error is eliminated in dual mode since the same air is used in both sides, thereby cancelling out the effect of any contaminants. Temperature changes or drifts within the oven 21 are elminated in that all conduits pass through the same temperature bath. Similarly, differences or anomalies in atmospheric pressure, other influences from within the analyzer, and the like, are all automatically compensated for in dual mode. v

Referring now to FIG. 2, diagram 54 represents a typical plot of temperature-pressure combustion of a hydrocarbon. For a fuller explanation reference may be had to the book entitled: Combustion, Flames and Explosions of Gases by Bernard Lewis and Guenther vanElbe, Academic Press Inc., New York, N.Y., copyright 1951. The line 56 in diagram 54 has a captured region within itself, and for ease of explanation the three regions defined by line 56 are labeled X to the left of the line, Y is the captured region, and Z for the region to the right of the line. The diagram 58 of FIG. 3 illustrates the conditions prevailing in the three regions X, ,Y and Z between the time the fuel and air are mixed, at the left, and the time when stable conditions are reached at the right hand terminus. Since explosions are not stable in the usual sense, stable conditions'* shall be understood to mean that condition which the reaction naturally seeks under the given temperature, pressure, and time conditions. Thus, it can be seen that the nature of the reaction or combustion of a hydrocarbon with air is dependent upon three factors, namely, the temperature, the pressure, and the elapsed reaction time. For example, beginning with a temperature and a pressure Which define a' point in region Z on diagram 54, reference to diagram 58 shows that as time proceeds the reaction progresses from a mild chemical reaction through the more vigorous cool flame reaction and finally stabilizes as an explosion. Because there are three factors, the invention could possibly operate in any of three zones, if the timing, controlled by actual time or speed of flow, was such that only a mild reaction Was permitted to exist. At the other extreme, choosing a temperature and a pressure which define a point in region X, diagram 58 indicates that a mild chemical reaction Will prevail regardless of elapsed time. Choosing points which fall in region Y, which is generally much narrower than either the X or the Z region, one can see that there is first a chemical reaction and then a cool flame after some elapsed time. It is in this region Y that the prior cool flame based techniques attempt to operate. The problem is obvious. Relatively small pressure changes will push the reaction, which such methods are attempting to hold as a cool flame, into region X extinguishing the cool flame, or into region Z thereby immediately causing an explosion. The reason such prior cool flame based techniques are inherently unstable is now apparent. On the other hand, the present invention chooses relatively low temperatures at atmospheric pressure to thereby assure operation in region X, to thereby achieve an inherently stable chemical reaction. Of course, the above description is a very much simplified explanation of a highly complicated technology. The cool flame is more correctly a non-steady state reacting system or a transient phenomenon, while the mild conditions of the present invention produces a steady more controlled reaction.

While the invention has been described in detail above, it is to be understood that this detailed description is by way of example only, and the protection granted is to be limited only within the spirit of the invention and the scope of the following claims.

We claim:

1. A method of determining the octane rating of a gasoline comprising the steps of continuously supplying a predetermined quantity of said gasoline, continuou-sly supplying a predetermined quantity of oxygen, mildly reacting said gasoline and said oxygen together under selected conditions including a temperature in the range of from about 275 C. to about 350 C., keeping the reaction less vigorous than a cool flame, measuring the quantity of oxygen consumed in said reaction, and correlating said measured amount of oxygen to the oc-tane rating of 'said gasoline.

2. The combination of claim 1, wherein said oxygen is supplied in an oxygen containing gas.

3. The method of claim 1 wherein said oxygen -is supplied in air.

4. The method of claim 1, wherein said reaction is carried out at about atmospheric pressure.

5. The method of claim 1, wherein said reaction is carried out at about 325 C.

6. The method of claim 1, wherein the amount of oxygen consumed is measured by measuring the amount of free oxygen in the reaction products, and by subtracting said amount of free oxygen from said predetermined amount of oxygen supplied.

7. The method of claim 1, and supplying a predetermined quantity of a standardized gasoline having a known value of octane rating, mildly reacting both of said gasolines separately from each other with equal quantites of oxygen, and comparing the quantites of oxygen consumed by both of said gasolines, whereby the comparison results yield the value of the octane rating of said first mentioned gasoline based on the known value of octane rating of said standardized gasoline.

8. Apparatus for determining the octane rating of a gasoline comprising reactor means, means to supply known quantites of said gasoline and of oxygen -to said reactor means, means to hold said reactor means at a predetermined temperature in the range of from about 275 C. to a'bout 350 C., and means to determine the quantity of oxygen consumed by said reaction.

9. The combination of claim 8, said determining means comprising means to measure the quantity of -free oxygen in the reaction products, whereby said quantity of oxygen consumed is determined by su-bstracting said quantity of free oxygen from said known quantity of oxygen supplied.

10. The combination of claim 8, said reactor means including a pre-heater portion and a reactor portion.

11. The combination of claim 8, wherein said predetermined temperature is about 325 C.

12. The combination of claim 8, wherein the oxygen is supplied in air.

13. The combination of claim 8, wherein said reaction is carried out at about atmospheric pressure.

14. The combination of claim 8, wherein said reactor means and said quantity determining means are of dual construction, means to supply known quantites of a standardized gasoline having a known Octane rating to half of said dual apparatus, and means to supply said first mentioned gasoline to the other half of said dual apparatus, means to split the supply of oxygen to supply equal quantities of oxygen to each half of said dual reactor means, said determining means including means to compare the quantites of oxygen consumed by the reacting of both of said gasolines, whereby the comparison results yield the octane rating of said first mentioned gasoline based on 7 8 the known value of Octane rating of said standardized 3,607,230 9/1971 Wintrell 23-230 PC gasoline. 3,627,467 12/1971 wiseman 23-230 Pc 't d References C' MoRRIs o. woLK, Primary Examiner UNITED sTATEs PATENTs R E SERWIN A t t E 3,463,631 8/1969 Vayssiere eta1. 23-230 Pc 5 S815 an mmm 3,s6o,1s6 2/1971 Tealetal 23-253 Pc U.s.c1.X.R.

3,582,281 6/1971 Fenske et al. 23-230* PC 23-4253 PC 

